The present invention relates to explosive devices, and more specifically to stab-initiated detonators or primers which contain a single explosive charge, namely, a uniform mixture of a major amount of mercuric-5-nitrotetrazole and a minor amount of tetracene.
It has been the general practice in the explosive arts to employ three different explosive charges of varying sensitivity in the design of conventional stab-initiated detonators. These charges are typically an ignition charge which possess the requisite stab sensitivity for initiating the detonator, an intermediate charge which builds rapidly from burning to detonation and which is positioned adjacent to the ignition charge, and a less sensitive but more powerful base charge which has a detonation velocity greater than that of the ignition or intermediate charges and which is positioned adjacent to the intermediate charge.
An example of an ignition charge which is typically employed in stab-initiated detonators is a primary mixture composed of 40% basic lead styphnate, 20% barium nitrate, 20% lead azide 15%, antimony sulphide and 5% tetracene. Another commonly used ignition charge is a priming mixture composed of 33.4% potassium perchlorate, 33.3% antimony sulphide, 28.3% lead azide, and 5.0% carborundum. Intermediate charges which are commonly used in stab-initiated detonators are dextrinated lead azide, or lead azide (PVA) which is lead azide that has been precipitated in the presence of polyvinyl alcohol. Conventional base charges for stab-initiated detonators include 2,4,6,N-tetranitromethylaniline (tetryl), pentaerythritol tetranitrate (PETN) and cyclotrimethylenetrinitramine (RDX).
One disadvantage of using three separate charges in the construction of detonators is that they must be placed in a definite order of varying sensitivity within a cup or container. Where loading of these containers is done on a large scale and there are many charges of varying sensitivity used in loading, errors could obviously arise in the order of sensitivity in which these charges are packed in the container, and such errors in turn would cause a misfiring, or render the detonator inoperative.
Another disadvantage in using three components in a single detonator is that the sensitivities and component lengths of the ignition charge, the intermediate charge and the base charge must be predetermined in relation to one another to optimize the explosive transition from the very sensitive primary charge to the less sensitive base charge.
In the past, attempts have been made to reduce the number of separate explosive charges present in detonators of various types. For example, see U.S. Pat. No. 1,968,134 to Eschbach et al. and U.S. Pat. No. 3,340,808 to Leopold. However, none of the efforts disclosed in the prior art have led to the successful development of a stab-initiated detonator employing a single explosive charge.
Thus, the general purpose of the present invention is to provide a stab-initiated detonator employing a single explosive charge which is comparable in stab sensitivity and output to three component prior art detonators, and which possesses none of the aforementioned disadvantages of three component detonators. A detonator employing a single explosive charge will result in a decrease in the number of charges needed, as compared to prior art stab-initiated detonators. The determination of appropriate column lengths for the various charges, as mentioned above, will be obviated. Loading errors will be totally eliminated. The loading time involved in manufacturing stab initiated detonators will be greatly reduced, and the overall manufacturing procedure will be simplified.